EP0854636B1 - Filtres hiérarchiques par comparaison avec des motifs standards - Google Patents

Filtres hiérarchiques par comparaison avec des motifs standards Download PDF

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Publication number
EP0854636B1
EP0854636B1 EP98300400A EP98300400A EP0854636B1 EP 0854636 B1 EP0854636 B1 EP 0854636B1 EP 98300400 A EP98300400 A EP 98300400A EP 98300400 A EP98300400 A EP 98300400A EP 0854636 B1 EP0854636 B1 EP 0854636B1
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Prior art keywords
pixel
windows
pattern
image
pixels
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EP98300400A
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German (de)
English (en)
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EP0854636A2 (fr
EP0854636A3 (fr
Inventor
Robert P. Loce
Michael Branciforte
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Xerox Corp
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Xerox Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40—Picture signal circuits
    • H04N1/40068—Modification of image resolution, i.e. determining the values of picture elements at new relative positions
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T5/00—Image enhancement or restoration
    • G06T5/20—Image enhancement or restoration using local operators

Definitions

  • This invention relates generally to hierarchically organized filters for processing digital images, and more particularly to the use of hierarchically organized template-matching filters to accomplish the resolution enhancement in a cost and computationally efficient manner.
  • US-A-4,437,122 to Walsh et al. describes a method of resolution enhancement for a system receiving video display pixel information and providing hard copy output. Enhancement is achieved by storing successive lines of video data in parallel shift registers, applying the output of the shift registers to a decoder, and generating driving signals for a printer head.
  • the decoder "compares the pixels on the same lines as well as in preceding and succeeding lines that surround each specific input pixel to generate the printer head driving signal according to whether straight or curved line segments are to be formed" (col. 2, lines 6-10).
  • enhancement of the central pixel may be determined by "progressively examining an ordered table of matches to find an equivalent image and its related enhancement" (col. 3, line 67 - col. 4, line1).
  • the present invention is adaptable to apply template matching in any system that utilizes multiple patterns in a matching algorithm.
  • Some common applications include enhancement of digital documents, resolution conversion and enhancement of digital documents, image restoration for aesthetic purposes, or human and machine recognition (e.g., OCR, and other feature recognition).
  • Template matching has been effectively employed to overcome some of the sampling errors that are caused by the use of input data that is too coarse to accurately represent the higher spatial frequency content of an image.
  • coarseness refers to sampling in a manner that does not fully represent the information content of the image, which includes coarse spatial sampling (e.g., spots per inch(SPI)), and coarse quantization (e.g., 1 bit/pixel compared to 8 bits/pixel).
  • a specific application in which the present invention finds particular use is enhancement of images for electronic printing.
  • digital character features are often recognized and based upon the recognition and capability of the image writing member, various types of enhanced pixel signals are generated and used to write the final printed or displayed image.
  • Types of enhanced signals include increased quantization range (conversion of binary signal to gray-scale, which is commonly referred to as antialiasing), high addressable signals that control the writing spot over distances smaller than the spot itself, and pulse controlled signals that may activate the writing member (e.g. laser) some preferred length of time that may be shorter than a nominal pixel period.
  • High-addressability printers operate by scanning one or more intensity modulated scan spots over a high gamma, photosensitive recording medium in accordance with a scan pattern that causes the spot or spots to superimpose displaced multiple discrete exposures on the recording medium.
  • High addressability typically refers to the ability to address the image writing member (e.g. laser) in spatial increments finer than the size of the writing spot, or nominal resolution of the imaging system.
  • High addressability systems have substantially linear edge position responses, so that pixel signals modulated in accordance with the preselected values are used by these systems for spatially positioning the transitions that are contained by the images they render to a sub-pitch (smaller than the writing spot) precision.
  • US-A-5329599 describes an image enhancement process in which a pixel pattern is identified within an image and then that pixel pattern is compared with a number of known pixel patterns or templates. This generates a list of potential matches and the template with the highest priority is determined as the matching template and the central pixel of the original pixel pattern is then enhanced in accordance with the chosen template.
  • a method of enhancing the contour fidelity of reproduction of an image represented by a plurality of pixels comprising the steps of:
  • filter windows have been described as having a common target pixel, it is understood by those skilled in the art that the concepts are immediately extendible to windows that contain a plurality of common pixels. Use of multiple common pixels in window mapping is referred to as area mapping. See European application EP-A-744,861 for a description of an area mapping method that may employ the present invention.
  • an apparatus for enhancing an image represented by a plurality of pixels comprising:
  • a first of the plurality of windows consists of a window of a dimension NxN and a second of the plurality of windows comprises a window having at least one dimension greater than N.
  • N is equal to three.
  • the second of the plurality of windows is a more specific window, selected from group comprising, in increasing order of specificity:
  • One aspect of the invention is based on the recognition of a problem with conventional and high addressability printing utilized to render enhanced exposure fidelity to a photoreceptor or other recording media.
  • the source of the high fidelity information is a sampled image or a high resolution bitmap.
  • many raster data sources provide low resolution bitmaps at 300 or 400 bits per inch (12 or 16 bits/mm), which is not enough resolution to eliminate unwanted artifacts induced by the coarseness of the information, such as stairstepping.
  • resolution enhancement to improve such renderings is known, the present invention is directed to a computationally and cost-effective manner to achieve template-matching.
  • the hierarchical design of the invention has the advantage of simplifying and thereby reducing the cost and complexity of the implementation.
  • Pattern templates are implemented in a set of hierarchical windows, in which the more specific pattern that receives a match has priority over the smaller, more general patterns.
  • the patterns are arranged in accordance with the pattern size so as to reduce the storage necessary to implement the very specific patterns.
  • the technique described above is advantageous because it efficiently reduces the storage requirements of a template-based resolution enhancement system while maintaining the ability to recognize very specific template patterns.
  • resolution enhancement using hierarchical template-matching techniques may be accomplished with reduced template pattern storage.
  • An “image” is a pattern of physical light.
  • An image may include characters, words, and text as well as other features such as graphics, including pictures.
  • An image may be divided into "segments,” each of which is itself an image.
  • a segment of an image may be of any size up to and including the whole image.
  • An item of data "defines" an image when the item of data includes sufficient information to produce the image.
  • a two-dimensional array can define all or any part of an image, with each item of data in the array providing a value indicating the color of a respective location of the image
  • Each location in an image may be called a "pixel.”
  • each value indicating the color of a location may be called a "pixel value”.
  • Each pixel value is a bit in a "binary form” of an image, a gray scale value in a “gray scale form” of an image, or a set of color space coordinates in a "color coordinate form” of an image, the binary form, gray scale form, and color coordinate form each being a two-dimensional array defining an image.
  • a "central pixel” is not literally the center pixel in a region, rather the term describes a target pixel that a plurality of template windows have in common. It will be appreciated that many or all of the pixels become the "central" or "target” pixel during the process of enhancing an entire image.
  • a "high-addressability" pixel is a pixel for which the location and size of the mark to be rendered for the pixel can be controlled at a resolution higher than the pixel resolution.
  • a high-addressability pixel may be represented by a plurality of sub-pixels therein, where each subpixel may be rendered as black or white (color, no color). It will be appreciated by those skilled in the art that other methods of accomplishing high-addressability output may be dependent upon the marking engine employed, and that high-addressability is not necessarily limited to sub-pixel imaging techniques.
  • “Resolution enhancement” is a process by which the pixels of an image are processed to produce either more pixels for the same spatial region or the same number of high-addressability pixels.
  • An item of data "relates to" part of an image, such as a pixel or a larger segment of the image, when the item of data has a relationship of any kind to the part of the image.
  • the item of data could define the part of the image, as a pixel value defines a pixel; the item of data could be obtained from data defining the part of the image; the item of data could indicate a location of the part of the image; or the item of data could be part of a data array such that, when the data array is mapped onto the image, the item of data maps onto the part of the image.
  • An operation performs "image processing" when it operates on an item of data that relates to part of an image.
  • a "neighborhood operation” is an image processing operation that uses data relating to one part of an image to obtain data relating to another part of an image.
  • Pixels are "neighbors” or “neighboring” within an image when there are no other pixels between them or if they meet an appropriate criterion for neighboring. For example, using a connectivity criterion if the pixels are rectangular and appear in rows and columns, each pixel has 4 strong neighbors, 4 weak neighbors or a total of 8 neighboring pixels.
  • a "version" of a first image is a second image produced using an item of data defining the first image.
  • the second image may be identical to the first image, or it may be modified by loss of resolution, by changing the data defining the first image' or by other processes that result in a modified version.
  • An “image input device” is a device that can receive an image and provide an item or items of data defining a version of the image.
  • a desktop “scanner” is an example of an image input device that receives an image by a scanning operation, such as by scanning a document.
  • An “image output device” is a device that can receive an item of data defining an image and provide the image as output.
  • a “display” and a “laser printer” are examples of image output devices that provides the output image in human viewable form.
  • the visible pattern presented by a display is a "displayed image” or simply “image” while the visual pattern rendered on a substrate by the printer is a "printed image”.
  • ROSs Raster output scanners
  • a type of image output device developed for xerographic printing employ a single beam or a multi-beam laser light source for supplying one or more intensity modulated light beams, together with a scanner (such as polygon scanner) for cyclically deflecting the modulated laser beam or beams across a photoreceptor in a "fast scan direction" while the photoreceptor is being advanced simultaneously in an orthogonal "process direction.”
  • a scanner such as polygon scanner
  • each of the laser beams typically is brought to focus on or near the photoreceptor surface to provide a substantially focused "scan spot.”
  • the scan spot scans the photoreceptor in accordance with a predetermined scan pattern because the fast scan deflection of the laser beam or beams vectonally sums with the process direction motion of the photoreceptor.
  • the flying spot ROS scans a data modulated light beam 12 over a xerographic photoreceptor 14 in accordance with a predetermined raster scanning pattern.
  • the ROS comprises a laser diode 16 for emitting the light beam 12 in the visible or invisible (e.g., infrared) band of the spectrum, together with a polygon 18 that has a plurality of nearly identical, mirror-like exterior sidewalls or "facets" 20.
  • a part of system 10 is a motor 22 for rotating the polygon 18 about its central axis, as indicated by the arrow 24, at a substantially constant angular velocity.
  • the polygon 18 is optically aligned between the laser 16 and the photoreceptor 14, so its rotation causes the laser beam 12 to be intercepted and reflected from one after another of the polygon facets 20, with the result being that beam 12 is cyclically swept across the photoreceptor 14 in a fast scan direction.
  • the photoreceptor 14, is advanced (by means not shown) simultaneously in a generally orthogonal, process direction at a substantially constant linear velocity, as indicated by the arrow 26, so the laser beam 12 scans the photoresponsive surface 14 in accordance with a raster scan pattern.
  • the photoresponsive surface 14 is coated on a rotating drum 28, but it will be apparent that it also could be carried by a belt or any other suitable substrate.
  • the ROS also includes pre-scan optics 30 and post-scan optics 32 for bringing the laser beam 12 to a generally circular focus proximate the photoresponsive surface 14 and for providing any optical correction that may be needed to compensate for scanner wobble and other optical irregularities.
  • the optical aperture of the ROS is sufficiently large to avoid excessive truncation of the laser beam 12 because the beam 12 then comes to a generally circular or elliptical focus with a gaussian intensity profile.
  • the broader aspects of the instant invention are not limited to any specific scan spot geometry or intensity profile.
  • the amplitude, duty cycle, and/or pulse width of the laser beam 12 is preferably modulated (collectively referred to herein as "intensity modulation") in accordance with successive multi-bit digital data values.
  • These data values are clocked out of a data source 36 serially in response to data clock pulses that are time synchronized with the scan of the scan spot from bitmap location to bitmap location within the raster scan pattern.
  • the data clock frequency can be selected (by means not shown) to map the data onto the raster scan pattern at any desired magnification, using either the same or different magnifications in the fast scan and the process directions.
  • the data may be preprocessed in accordance with aspects of the instant invention as will be described herein for the printing of halftoned images, graphics and/or text and other types of line art, so that the data source 36 generically represents any suitable source of raster data for intensity modulating the laser beam 12.
  • the drive current for the laser diode 16 is serially modulated by modulator 38 in accordance with the data values that are clocked out of the data source 36, thereby intensity modulating the laser beam 12 at the data clock rate in accordance with those data values.
  • the fast scan positioning precision of the print engine 10 can be increased, if desired, by dynamically adjusting the frequency of the data clock to compensate for positioning errors that tend to be caused by, for example, variations in the angular velocity of the polygon 18 and facets 20, and localized variations in the geometric relationship of the polygon 18 to spatially distinct segments of any given scan line.
  • the clock may be used to control signals to the laser at a rate that yields spatial addressing of the scan spot at intervals finer than the spot itself.
  • This high addressability is the precise positioning of edges in a written image.
  • the present invention may find particular use in various image enhancement systems, for example, in resolution enhancement systems.
  • FIG 2 displayed therein is a block diagram illustrating the components of the data source 36 shown in Figure 1.
  • image input devices e.g., scanners
  • mass storage and networks local, intranet and internet
  • PDL page description language
  • Examples of PDLs include Interpress, PCL, and Postscript®, although documents represented by other PDLs or other formats are intended to be included as well.
  • Output of the PDL decomposer 52 is a bitmap image at a particular resolution, for example, 600 ⁇ 600 ⁇ 1 (SPI x SPI x bit/pixel).
  • the decomposer output is preferably further processed at resolution enhancer 54, where the digital image data is increased in resolution in at least one dimension.
  • the resolution enhancer would be employed to convert the PDL decomposer output from 600 ⁇ 600 ⁇ 1 to 2400 ⁇ 600 ⁇ 1 (i.e., 600 x 600 ⁇ 4) as depicted in Figure 2.
  • the enhanced resolution digital data would then be employed to control, on a sub-pixel or high-addressability basis, the modulation of the laser light source so as to render a resolution enhanced output.
  • Figure 3 is an exemplary block diagram illustrating the hierarchical nature of the resolution enhancer.
  • the data is passed to a pair of template or pattern matching filters 60 and 62.
  • the hierarchical pattern matchers would be implemented in parallel with one another as depicted in Figures 3 and 4 so as to maintain the performance of the resolution enhancement architecture.
  • pattern matching filters 60 and 62 data for a plurality of pixels located about a central pixel is compared to predefined patterns to identify a match. Whenever a match is detected, the pattern matchers output a resolution enhanced set of pixels or enhanced pixel signal for the central and surrounding pixels.
  • a hierarchical system is required. The system employed herein is one that gives preference to the larger, more specific pattern matching filters - in this example the 5 ⁇ 5 pattern matcher - using a multiplexer 64 controlled via a select line that indicates a match in the larger pattern matcher block.
  • Figures 5 and 6 where bitmap examples are depicted.
  • the 3 ⁇ 3 and 5 ⁇ 5 pattern windows are superimposed on one another; both centered about the central pixel C.
  • the 5 ⁇ 5 window contains significantly more image context than the smaller window.
  • the additional information of the larger window allows for a better estimate of the slope of an observed edge.
  • highly addressable signals are generated that are appropriate for enhancing the image to appear with the correct slope and without jagged transitions. A better estimate of the slope will yield a better appearing enhancement.
  • the slope estimation is implicit to the template design procedure.
  • the storage requirements for all possible patterns in the 5 ⁇ 5 window is significantly greater, 2 25 for the latter versus 2 9 for the former.
  • the present invention would employ the 5 ⁇ 5 patterns only where necessary to add context to the smaller set of 3 ⁇ 3 patterns.
  • bitmap 104 when compared to the enhancement that would have resulted if the 5 ⁇ 5 pattern match were employed to control the transition, bitmap 104, it is apparent that the transition should be spread over an even larger vertical range of pixels (e.g., pixels C -1 , C, C +1 ).
  • pattern matcher 62 not only outputs the enhanced pixel data generated in response to a recognized pattern, but a signal indicating that a match was present as well.
  • the match signal can then be employed as a select signal in the 2-input multiplexer 64 to select the 5 ⁇ 5 output whenever there is a match.
  • pattern matcher 62 can be optimized, using statistical techniques as described by Loce et al. in US-A-5,359,423 and US-A-5,387,985 so as to reduce the number of patterns to be recognized, thereby further reducing the pattern storage requirements of such a system.
  • resolution enhancer 54 is depicted in Figure 4.
  • additional hierarchical pattern matchers are depicted so as to further expand the ability to recognize and enhance particular patterns within the input image.
  • an orthogonal pair of template-matchers 70 and 72 have been added to the device depicted in Figure 3.
  • the 3 ⁇ 9 and 9 ⁇ 3 pattern matchers are particularly useful in identifying longer horizontal and vertical contour transitions, for example, as illustrated by bitmap 106 in Figure 6.
  • the present invention further encompasses alternative embodiments employing a number of other filter dimensions as represented by N ⁇ N pattern matcher 80.
  • Possible additional or alternative pattern matchers include, 7 ⁇ 7, 9 ⁇ 9, 7 ⁇ 3, 3 ⁇ 7, 7 5, 5 ⁇ 7, 9 ⁇ 5 and 5 ⁇ 9.
  • each of the pattern matchers would generate not only an enhanced output pixels in response to a match, but a match signal as well.
  • the match signals of an orthogonally paired pattern matcher are preferably mutually exclusive and may be combined by a simple logic circuit 74 so that only a single match signal is generated by the pair.
  • a preferred set may be 3x3, (5x3, 3x5), (7x3, 3x7), (9x3, 3x9)
  • Selection control logic 68 is pre-programmed to reflect the hierarchy of the template-matching filters.
  • the hierarchy of the selection logic would place enhancement by the more specific filters at a higher level, and the more general filters at a lower level.
  • the 9 ⁇ 3 or 3 ⁇ 9 pattern matchers would be selected over the orthogonal pairs 7x3, 3x7 and 5x3, 3x5, and over the smaller square windows 3 ⁇ 3, 5 ⁇ 5 or 7 ⁇ 7 pattern matcher.
  • the pattern matchers as depicted, operate in parallel so as to concurrently generate enhanced output in response to a common central pixel.
  • the system preferably operates at or above a data rate sufficient to provide the enhanced image data to printing system 10 at its processing speed.
  • the present invention is a method and apparatus for enhancing the contour fidelity of an image represented by a plurality of pixels, by storing pixel values representing a segment of the image in memory; isolating a plurality of regions of the pixels of said image segment to form a plurality of windows including a central pixel and a plurality of pixels surrounding said central pixel. Then comparing at least two of the regions of pixels within the windows with a set of standard pixel patterns for each of the windows and identifying matching pixel patterns within each of the windows.
  • pattern matching is not restricted to binary images. Gray-scale pattern matching and patterning matching in color imagery is also comprehended by the present invention.
  • pattern match is not restricted to an ideal one-to-one correspondence. Rather, it refers to matching to a significant degree as determined by some decision making criterion, as is understood in the fields of image region classification, statistical decision making, and others.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Image Processing (AREA)
  • Editing Of Facsimile Originals (AREA)
  • Picture Signal Circuits (AREA)
  • Facsimile Image Signal Circuits (AREA)

Claims (10)

  1. Procédé d'accentuation de l'image représentée par une pluralité de pixels, comprenant les étapes consistant à :
    (a) mémoriser des valeurs de pixel représentant un segment de l'image en mémoire ;
    (b) isoler une pluralité de régions des pixels dudit segment d'image pour former une pluralité de fenêtres, chaque fenêtre étant de dimension différente tout en incluant un pixel cible commun et des différentes pluralités respectives de pixels entourant le pixel cible ;
    (c) comparer au moins deux des régions des pixels à l'intérieur de la fenêtre à un ensemble de motifs du pixel standard pour chacune des fenêtres, chaque motif du pixel standard correspondant à un motif du pixel accentué prédéterminé ;
    (d) identifier les motifs du pixel correspondant à l'intérieur de chacune des fenêtres ; et
    (e) soit (i) accentuer le pixel cible en conformité avec le motif du pixel accentué du motif de pixel standard correspondant lorsque le pixel cible est positionné à une position corrigible dans seulement une des fenêtres, soit (ii) accentuer le pixel cible lorsque le pixel cible est positionné à une position corrigible dans une pluralité des fenêtres dans lequel l'accentuation est accomplie en conformité avec le motif de pixel accentué d'un des motifs de pixel standard correspondant déterminé en conformité avec une hiérarchie prédéterminée pour les fenêtres.
  2. Procédé selon la revendication 1, dans lequel l'étape (c) comprend l'opération consistant à comparer lesdites au moins deux des régions du pixel à l'intérieur des fenêtres simultanément.
  3. Procédé selon la revendication 1 ou 2, dans laquelle la hiérarchie prédéterminée est dans l'ordre des motifs du pixel spécifique aux motifs du pixel généraux et où les motifs du pixel généraux sont représentés par des fenêtres qui sont plus petites que les fenêtres associées au motif de pixel spécifiques.
  4. Procédé selon la revendication 1, 2 ou 3, dans lequel l'étape (e) comprend l'opération consistant à appliquer l'accentuation au pixel cible et au moins à un pixel voisin.
  5. Procédé selon la revendication 4, dans lequel l'étape (e) a pour résultat l'accentuation d'une pluralité de pixels entourant le pixel cible.
  6. Appareil pour accentuer l'image représentée par une pluralité de pixels, comprenant :
    une mémoire pour stocker les valeurs des pixels représentant un segment de l'image ;
    un moyen pour isoler une pluralité de régions des pixels dudit segment d'image pour former une pluralité de fenêtres, chaque fenêtre étant de dimensions différentes tout en incluant un pixel cible commun et des pluralités respectives de pixels entourant ledit pixel cible ;
    une pluralité de dispositifs de correspondance de motif (60, 62, 70, 72, 80) pour comparer au moins deux des régions du pixel à l'intérieur des fenêtres à un ensemble de motifs de pixel standards pour chacune des fenêtres et pour signaler la présence de motifs de pixel correspondant à l'intérieur de chacune des fenêtres ; chaque motif du pixel standard correspondant à un motif de pixel accentué prédéterminé ; et
    ledit dispositif de correspondance de motif étant conçu pour soit (i) accentuer le pixel cible lorsque le pixel cible est positionné à une position corrigible dans seulement une des fenêtres en conformité avec le motif de pixel accentué du motif du pixel standard correspondant, soit (ii) accentuer le pixel cible lorsque le pixel cible est positionné à une position corrigible dans une pluralité de fenêtres, dans lequel l'accentuation est accomplie en conformité avec le motif de pixel accentué d'un des motifs du pixel standard correspondant déterminé en conformité avec une hiérarchie prédéterminée pour les fenêtres.
  7. Appareil selon la revendication 6, dans lequel la pluralité des dispositifs de correspondance de motif (60, 62, 70, 72, 80) sont conçus pour fonctionner simultanément sur les pixels à l'intérieur des fenêtres.
  8. Appareil selon la revendication 6 ou 7, dans lequel la hiérarchie prédéterminée est dans l'ordre des motifs du pixel spécifique aux motifs de pixel généraux et où les motifs de pixel généraux sont représentés par des fenêtres qui sont plus petites que les fenêtres associées au motif du pixel spécifique.
  9. Appareil selon la revendication 6, 7 ou 8, dans lequel les dispositifs de correspondance de motif (60, 62, 70, 72, 80) sont conçus pour modifier le pixel cible et au moins un pixel voisin.
  10. Appareil selon l'une quelconque des revendications 6 à 8, dans lequel les dispositifs de correspondance (60, 62, 70, 72, 80) sont conçus pour accentuer une pluralité de pixels entourant le pixel cible.
EP98300400A 1997-01-21 1998-01-20 Filtres hiérarchiques par comparaison avec des motifs standards Expired - Lifetime EP0854636B1 (fr)

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Application Number Priority Date Filing Date Title
US784636 1997-01-21
US08/784,636 US6332044B1 (en) 1997-01-21 1997-01-21 System and method for enhancement of image contour fidelity

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EP0854636A2 EP0854636A2 (fr) 1998-07-22
EP0854636A3 EP0854636A3 (fr) 1999-05-12
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US6332044B1 (en) 2001-12-18
DE69801931T2 (de) 2002-04-04
JP3923640B2 (ja) 2007-06-06
EP0854636A2 (fr) 1998-07-22
EP0854636A3 (fr) 1999-05-12
JPH10224603A (ja) 1998-08-21
DE69801931D1 (de) 2001-11-15

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